Lead is a toxic heavy-metal pollutant which is hazardous to human health and the environment. Sodium nitroprusside is commonly used as a nitric oxide donor in plants. Nitric oxide is a bioactive molecule playing an important role in response to stress in plants. Weight, chlorophyll content, and the activity of catalase (EC 1.11.1. 6) and peroxidase (EC 1.11.1. 7) antioxidant enzymes of canola (Brassica napus L.) Hyola 401 in lead stress were investigated. This study tested the hypothesis that sodium nitroprusside plays an ameliorating role under lead-toxicity in canola. For seven days, thirteen-day plants were exposed to two levels of sodium nitroprusside (0 and 100 µM) and three levels of lead (0, 100, and 200 µM). Dry and fresh weight and chlorophyll content were decreased in lead stress, while sodium nitroprusside treatment increased weight and chlorophyll b in the same conditions. Lead stress increased the activity of antioxidant enzymes, and sodium nitroprusside treatment reduced their activity. The results showed that the use of sodium nitroprusside reduces lead toxicity. Manuscript profile